The present disclosure relates to a liquid crystal lens using liquid crystal molecules having refractive anisotropy to generate a lens effect, and a display device using the liquid crystal lens.
In the past, a binocular or multi-view stereoscopic display device, which achieves stereoscopy through presenting a parallax image to both eyes of a viewer, has been known. As a method for achieving such a stereoscopic display device, for example, a two-dimensional display device such as liquid crystal display is combined with an optical device (parallax separation unit) for three-dimensional display for deflecting display image light from the two-dimensional display device in a plurality of view angle directions. As the optical device for three-dimensional display, a cylindrical lens array (lenticular lens) 302, including a plurality of cylindrical lenses 303 arranged in parallel, is used, for example, as shown in FIG. 18. The lenticular lens 302 is disposed opposite a display surface of a display panel 301 including the two-dimensional display device. Each cylindrical lens 303 is arranged to extend in a longitudinal direction to the display surface of the display panel 301 so as to have refracting power in a lateral direction. A plurality of display pixels are regularly arranged in a two-dimensional manner on the display surface of the display panel 301. Two or more pixels are disposed behind one cylindrical lens 303, and beams emitted from the pixels are directed in different horizontal directions by refracting power of the lens to meet binocular parallax, thereby enabling naked-eye stereoscopy.
FIG. 18 shows an example of binocular stereoscopic display, where adjacent two pixel arrays 301R and 301L on the display surface of the display panel 301 are allocated to each cylindrical lens 303. One pixel array 301R displays a right-parallax image, and the other pixel array 301L displays a left-parallax image. Each of the displayed parallax images is directed to a laterally separated light path 402 or 403 by each cylindrical lens 303. Consequently, when a viewer 400 views such a stereoscopic display device in a predetermined direction and from a predetermined position, the right and left parallax images appropriately reach right and left eyes of the viewer 400, respectively, and the viewer thus senses a stereoscopic image.
Similarly, for multi-view stereoscopic display, a plurality of parallax images, which are taken at positions and in directions corresponding to three or more visual points, are evenly allocated and displayed within a lateral lens pitch of the cylindrical lens 303. Consequently, three or more parallax images are emitted in continuous, different angle ranges and focused by the lenticular lens 302. In this case, a plurality of different parallax images are sensed in correspondence to positions and directions of changed visual lines of the viewer 400. A more realistic stereoscopic effect may be obtained with increase in number of the parallax images in correspondence to changed visual points.
As the lenticular lens 302, for example, a resin-molded lens array, which is fixed in shape and thus fixed in lens effect, may be used. In this case, since the lens effect is fixed, a special display device for three-dimensional display is given. A switchable lens array element with a liquid crystal lens may be also used as the lenticular lens 302. In the case of the switchable lens array element with a liquid crystal lens, since presence or absence of a lens effect may be electrically switched, a display mode may be switched between two display modes, namely, two-dimensional display mode and three-dimensional display mode, through combining the lens array element with a two-dimensional display device. In other words, in the two-dimensional display mode, the lens array is set to be in a no-lens-effect state (no-refracting-power state) so as to transmit display image light from the two-dimensional display device without any change. In the three-dimensional display mode, the lens array is set to be in a lens-effect state so as to deflect the display image light from the two-dimensional display device in a plurality of view angle directions, so that stereoscopy is achieved.
A configuration example of the switchable (variable) lens array element with a liquid crystal lens is described with reference to FIGS. 19A and 19B. The figures mainly show a structure of an electrode portion while omitting other components such as a substrate and an alignment film. Moreover, the figures show the configuration in a simplified manner for illustrating a principle of generation of a lens effect in the lens array element. The variable lens array element includes transparent first and second substrates made of, for example, a glass material, and a liquid crystal layer 130 sandwiched between the first and second substrates. The first and second substrates are oppositely disposed with a space d.
A first electrode 111 including a transparent conductive film such as an ITO (Indium Tin Oxide) film is uniformly formed over almost the whole surface on the first substrate. In addition, a first alignment film is formed on the first substrate in a manner to contact with the liquid crystal layer 130 via the first electrode 111. Second electrodes 121Y including a transparent conductive film such as an ITO film are partially formed on the second substrate. In addition, a second alignment film is formed on the second substrate in a manner to contact with the liquid crystal layer 130 via the second electrodes 121Y.
The liquid crystal layer 130 includes liquid crystal molecules 131, where an alignment direction of the liquid crystal molecules 131 is changed depending on voltage applied by the first electrode 111 and the second electrodes 121Y, so that the lens effect is controlled. Each liquid crystal molecule 131 has refractive anisotropy, and thus, for example, has a structure of an optical indicatrix having different refractive indexes to a passing beam between a long-side direction and a short-side direction. The liquid crystal layer 130 is electrically switched between a no-lens-effect state and a lens-effect state depending on voltage applied by the first electrode 111 and the second electrodes 121Y.
In the lens array element, as shown in FIG. 19A, the liquid crystal molecules 131 are uniformly aligned in a predetermined direction defined by the first and second alignment films in a normal condition with applied voltage of 0 V. Therefore, a wave front 201 of a passing beam is a plane wave, showing the no-lens-effect state. In the lens array element, since the plurality of second electrodes 121Y are separately arranged from one another with a predetermined space, when a predetermined drive voltage is applied between the first electrode 111 and the second electrodes 121Y, deviation occurs in electric field distribution within the liquid crystal layer 130. In other words, an electric field is generated such that field strength is increased in accordance with the applied drive voltage in a portion corresponding to a region where each second electrode 121Y is formed, and decreased in a portion nearer to the center of an opening between the plurality of second electrodes 121Y. Therefore, alignment of the liquid crystal molecules 131 is changed in accordance with field strength distribution as shown in FIG. 19B. Consequently, the wave front 202 of a passing beam is changed, leading to a lens-effect generation state.
Such a variable lens array element may be used to equivalently generate a lens effect of a lenticular lens. Consequently, switchable display may be made between two-dimensional display mode and three-dimensional display mode.
Recently, a liquid crystal lens, which uses such an optical characteristic of a liquid crystal changed depending on applied voltage, has been increasingly developed. Use of a liquid crystal eliminates need of mechanically movable portions, which contributes to reduction in size and weight of a lens unit. “Switchable electro-optic diffractive lens with high efficiency for ophthalmic applications”, PNAS, 103, 16, 2006, pp. 6100-6104 proposes a method to generate a Fresnel-lens-like lens effect by a liquid crystal lens in order to widen an aperture of a lens and to improve performance of the lens. In the above non-patent document, an electrode is patterned in a concentric configuration to generate the Fresnel-lens-like lens effect. Japanese Unexamined Patent Application Publication No. 63-249125 and Japanese Unexamined Patent Application Publication No. 5-100201 also describe methods to generate a Fresnel-lens-like lens effect by using a liquid crystal. A liquid crystal lens is formed like a Fresnel lens as in the non-patent document, and therefore an aperture may be widened and besides the amount of liquid crystal material to be used may be decreased, leading to reduction in cost. Furthermore, the non-patent document describes an example of achieving glasses using the liquid crystal lens.